1. Field of the Invention
The present invention relates to a photographic film cassette and a method of manufacturing the same. More particularly, the present invention relates to an improvement of a photographic film cassette in which a leader of a photographic film is caused, by rotation of a spool, to advance to the outside of a cassette shell, and a method of manufacturing the cassette.
2. Description of the Related Art
As suggested in U.S. Pat. No. 4,834,305, a known photographic film cassette includes a photographic film positioned so that a leader does not protrude from the cassette prior to loading the cassette in a camera. Such a cassette is easily loaded into a camera. A simple film-advancing mechanism of the camera is typically used with this type of cassette, and includes a construction which rotates a spool to unwind a photographic film strip (hereinafter referred to as film), thereby causing the leader to move through a passageway for the photographic film and exit from the cassette.
The passageway is a slot defined between a pair of gapped portions formed on a pair of cassette halves. Light-shielding members are attached to the inside of the gapped portions in order to prevent ambient light from entering the cassette shell. The light-shielding member are, for example, a fabric of high resilience, such as plush or teremp cloth. If the cassette shell is made of resin, the light-shielding members can be welded to the passageway by ultrasonic welding, wherein an ultrasonic wave is applied for melting the resin, and the light-shielding members are pressed against the melted portions. Such a method is convenient and advantageous in that no adhesive agent is required.
It is important to minimize frictional forces between the light-shielding members and the photographic film 4 in order to minimize the torque required for outward advancement of the leader. Various manners of attaching the light-shielding members to the passageway have been proposed. For example, in a commonly assigned copending application U.S. Ser. No. 07/897,058. As illustrated in FIG. 20, light-shielding members 107 and 108 are welded to passage surfaces 101 and 102 of a pair of gapped portions 109a and 109b interior from a passage mouth 6 by an ultrasonic welding device. Innermost portions 103 and 104 of the light-shielding members 107 and 108 are welded by a welding horn of the welding tool, and are spaced so as to be kept from contact with photographic film 4. Innermost attaching portions 101a and 102a of passage surfaces 101 and 102 are such that advancement of the photographic film 4 does not come into contact with innermost portions 103 and 104.
To keep the light-shielding members 107 and 108 nearly free from creases and irregularities and improve light-shielding performance, light-shielding members 107 and 108 consist of fabrics 107a and 108a which are 0.1 mm thick, and respective soft polyurethane sponges 107b and 108b which are 3.1 mm thick as measured under the application of a load of 5 g/cm.sup.2. Facing surfaces of the fabrics 107a and 108a have frictional coefficients of 0.25 or less with respect to the photographic film 4. Their compressibility is such that a different R, between T.sub.1 and T.sub.2, satisfies the condition 0.6 mm&lt;R&lt;4.0 mm, wherein the light-shielding members are T.sub.1 thick under a load of 100 g/cm.sup.2, and be T.sub.2 thick under a load of 20 g/cm. A polyester thread of 70 denier consisting of 20 filaments is woven to be a fabric of plain weave, in which a warp thread density is 90 threads/inch and a weft thread density is 120 threads/inch. The fabric of the plain weave is dyed by a black dispersed dye of 5% on the weight of fiber (o.w.f.), and then subjected to antistatic treatment by Parmalose.TM. (trade name; manufactured by ICI Ltd.) of 4% o.w.f.
Should a considerable area of a light-shielding member be welded by ultrasonic welding, resilience of the member would be lowered. The construction disclosed in the above document has the purpose of maintaining the initial resilience even after welding, by limiting welding to the innermost portions on the slanted surfaces 101a and 102a.
However, there is a problem in the above-mentioned construction in that the frictional forces between the photographic film 4 and the light-shielding members 107 and 108 are too high when the photographic film 4 is withdrawn or rewound up into the cassette shell. Except for the innermost portions, the light-shielding members 107 and 108 are unattached from the passageway and thus come into contact with the photographic film 4 over a relatively large area when it is rewound, and are therefore highly resistant to movement of the film, as illustrated in FIG. 21 (where gaps between the light-shielding members 107 and 108 are the attaching portions 101 and 102 are exaggerated for convenience in understanding). The load on the spool of the cassette is thus enlarged, and a motor in a camera may operate poorly or be damaged. Even after rewinding up the photographic film 4 in such a device, the light-shielding performance can be degraded and the leader can fail advance even, when the spool is rotated in the unwinding direction, because of the deformation of light shielding members 107 and 107 as indicated in FIG. 21.
If the ultrasonic welding device is applied to the entire surfaces of the light-shielding members 107 and 108, the light-shielding members 107 and 108 may be melted and their resilience lowered.